On 2 December 2013 the American Meteorological Society joined the American Institute of Physics. Among the benefits that AIP offers to AMS and its other member societies is Physics Today. Eager to meet the magazine’s new community of readers, I attended the annual meeting of the AMS, which took place earlier this week in Atlanta.
My first impression of meteorologists was positive. On my first walk from my downtown hotel to the Georgia World Conference Center, I met a graduate student from the University of Oklahoma. She graciously put up with my basic questions about AMS and meteorology. From her I learned, among other things, which journals meteorologists favor (mostly those of the AMS, it turns out).
The annual meeting kicked off with a student conference. Several hundred meteorology students gathered to learn about how to turn their studies into careers. In one session, students were assigned to small groups in one of two categories: weather reporters and emergency responders. Then, the session's presenters took their audience through three historical events of extreme weather. The presenters paused at various moments to challenge the young meteorologists to decide what advice, advisories, and warnings to issue.
The group of students I was sitting next to were pretending to be weather reporters during what looked like an increasingly bad rain storm. It turned out to be the 2009 Southeastern US floods that inundated Atlanta and other parts of Georgia, damaged 20 000 buildings, and killed 10 people. The group's coach was a real weather reporter (and AMS member), Brad Nitz of Atlanta-based ABC affiliate WSB-TV.
At its most intense, the rain storm that beset Georgia on 15–23 September 2009 dumped 16 inches of rain in 16 hours. CREDIT: Time photos
Nitz explained that whereas weather forecasters can predict what will fall from the skies, it’s up to weather reporters to use their local knowledge to transform the data into predictions of what will happen on the ground: Which creeks will flood? Which neighborhoods will get cut off? The session was captivating, especially when Nitz commented on archival footage from his station's coverage of the flood.
One of the session's organizers, a graduate student from the University of Michigan, explained that the idea for the session originated from a similar exercise put on at the central Iowa conference of the National Weather Association. But this time, she said, the students did not have computers at their disposal. They had to use only the data that were presented to them and to reach a plan of action by talking among themselves.
The next day, having walked once to the convention center from my hotel, I was able to help a meteorologist whom I bumped into on Peachtree Street. He had just arrived in Atlanta and was wondering how to get to the meeting. We walked there together.
My walking companion was Bob Baxter, who’s a principal at a company called T&B Systems based in a Valencia, California. T&B, Baxter explained, sells environmental monitoring services. Among his customers are local and state governments that need help satisfying various regulations. Baxter wasn’t attending AMS to meet customers, he told me. Rather, his main mission was to find out about the latest monitoring technologies from companies that exhibit at the meeting.
The presence of T&B and other private-sector companies at the meeting was a surprise to me, but presumably not to AMS members. More than one session talked about the “weather enterprise,” meaning the ecosystem formed by for-profit companies, academic departments, and government agencies. Indeed, the AMS logo explicitly recognizes the importance of meteorology to industry and commerce.
For me, the weather enterprise was personified by a meteorologist whom I met on my way back to the hotel. Gerry Mulvey used to work for Northrop Grumman. Now he’s a professor at the University of the Incarnate Word in San Antonio, Texas. Mulvey told me about his latest project: mapping the heat island effect over San Antonio using a fleet of drones flying in formation. The project has the city’s backing. And thanks to his connections in the aerospace industry, Mulvey is able to buy sensors that failed to qualify for the rigors of space but are still good enough for the rigors of a San Antonio summer.
One of the hardest physics problems in meteorology concerns how aerosols—small airborne particles —influence the formation and nature of clouds. But I didn’t have to go to the AMS meeting to find that out. Ten years ago, I wrote a news story for Physics Today about a pair of experiments that evaluated the impact of aerosols in the Amazon during tree-burning season.
For an update on the topic, I attended a session called Aerosol–Cloud Interactions in Shallow Cumuli, Stratiform, and Cirrus Clouds I. Two of the talks were about a project called CARRIBA, which undertook measurement campaigns in Barbados in 2010 and 2011.
Like other Caribbean islands, Barbados lies in the path of the easterly trade winds. As the easternmost island, Barbados has remarkably stable atmospheric conditions. The small puffy clouds that form off the island’s east coast constitute a perfect natural laboratory. That's because their principal perturbations come not from nature but from manmade aerosols, whose emission is sporadic.
In their respective talks, Holger Siebert and Florian Ditas of the Leibniz Institute for Tropospheric Research in Leipzig, Germany, explained how CARRIBA gathers data. A helicopter flies above the small puffy clouds. Trailing from a line that hangs beneath the chopper are two devices that look like winged torpedoes: One flies above the cloud and measures the light reflected off the top of the cloud; the other flies through the cloud and measures atmospheric conditions while scooping up and characterizing whatever aerosols are present. Thanks to the helicopter's low speed, the sampling pattern is dense and the data are rich.
As if to make the challenge of understanding aerosol–cloud interactions even harder, the CARRIBA team's principal finding is that size and density distributions of cloud droplets in trade wind cumuli are very sensitive to changes in size and density distributions of aerosols. What accounts for that sensitivity remains an open question.
The session was not my only encounter with aerosols. While I was walking through the posters in the exhibit hall I bumped into Danny Rosenfeld of Hebrew University in Jersusalem. Rosenfeld was a member of one of the teams whose work in the Amazon I’d covered in 2004. Back then, the team had flown a small instrument-laden plane through clouds whose formation had been strongly influenced by the sooty aerosols from burning.
The researchers had discovered that the aerosols boost the concentration of droplets that are too small to precipitate. Because rain cools clouds, thermal updrafts within the clouds become stronger. The small droplets and the sooty aerosols are carried higher into the atmosphere than they would otherwise reach in clean air.
What eventually happens to the small droplets and aerosols wasn't clear in 2004. The team's plane lacked the altitude to sample the cloud tops. This year, thanks to the use of a jet, Rosenfeld and his colleagues hope to determine whether the lofted droplets and aerosols have a substantial effect on regional and global circulation, as they suspect.
Rosenfeld also told me that the concept of soot-induced storminess had acquired the name "invigoration." Surprisingly, invigoration could turn out to help mitigate the devastating effects of hurricanes and typhoons. Seeding the outer regions of a hurricane with aerosols could cause it to rain there more vigorously, thereby drawing energy from the storm's center of the storm and ultimately making the storm less destructive.
When meteorologists convene, hurricanes, tornadoes, droughts, and other examples of extreme weather are a major focus for discussion. That’s not surprising. Such events kill people and damage buildings and crops. Still, as I walked past poster after poster about extreme weather, I became determined to find one devoted to nice weather. I found two.
The first was by Natalie Theeuwes of Wageningen University in the Netherlands and her colleagues. They had set themselves the task of evaluating whether the ornamental fountains, ponds, and lakes that are part of the urban environment of many cities improve thermal comfort.
The results of Theeuwes's numerical study are perhaps counterintuitive. Whereas bodies of water do lower the temperature, they also raise the humidity. Of the two effects, the increase in humidity prevails: Urban bodies of water reduce thermal comfort. Lakes, ponds, and fountains remain attractive features of cityscapes. But their virtue, it seems, is mostly aesthetic.
This historic apartment building occupies 13–15 Hajos Street in Budapest. CREDIT: Apartments in Budapest
The second pleasant weather poster was by Csilla Gal, an architecture student from the Chicago campus of the University of Illinois. Gal evaluated three basic styles of city block found in Budapest, Hungary: dense groups of houses, block-sized buildings that have a central courtyard, and isolated tower blocks. Using a numerical model, she evaluated the heat and humidity in the blocks' immediate neighborhood. Among her findings: The courtyard-style block is cooler in summer.
Like the other societies, AMS is keenly interested in the history of its field. The last session I attended at the meeting bore the title Perspectives on Climate and Weather Analyzed Through the Lens of History.
All the talks in the session were interesting. My favorite was by Daniel Burkhard of the University of Bern in Switzerland. During World War I, neutral Switzerland's import and export of food was disrupted. For the first two years of the war, 1914–15, the Swiss had enough to eat, but the very cold and wet summers of 1916–17 caused crops to fail.
Food prices inevitably rose, which provoked tension between rural and urban Swiss. City dwellers blamed the increases on farmers hoarding food; farmers blamed the weather. Exacerbating the problem was the focus of Swiss argiculture on producing chocolate and dairy products for export.
The widespread malnutrition that followed the crop failures exposed the fragility of Switzerland's food supply. It also prompted the Swiss government to take a series of measures to make the country more self-sufficient. Marginal land was converted to farmland. To reduce urban–rural tensions, farmers were encouraged to sell food directly to city dwellers.
The measures paid off. When in 1939 Europe became engulfed in another, longer war, the Swiss had enough to eat.